• Shunya Hanakita, Masahiro Shin, Tomoyuki Koga, Hiroshi Igaki, and Nobuhito Saito.
• Department of Neurosurgery, The University of Tokyo Hospital, Tokyo, Japan. Electronic address: hanakita-s@umin.ac.jp.
• World Neurosurg. 2016 Mar 1; 87: 242-9.

ObjectiveTreatment of extremely large cerebral arteriovenous malformations (AVMs) is challenging. Although volume-staged stereotactic radiosurgery (SRS) is a possible multimodal treatment option for such lesions, reports of these procedures are scarce. We evaluated the efficacy and safety of volume-staged SRS in patients with AVMs >20 cm(3) with >3 years of follow-up.MethodsBetween 2005 and 2012, 18 patients with AVMs >20 cm(3) were treated by volume-staged SRS. The median target volume was 38 cm(3) (interquartile range, 31-53 cm(3)). Treatment was conducted in 2-3 stages with a median interval of 6 months.ResultsThe median follow-up period from the last SRS treatment was 53 months (interquartile range, 41-75 months). Complete nidus obliteration was achieved in 6 patients (33%), and the obliteration rate at 5 years after initial SRS was 35% by the Kaplan-Meier method. The annual hemorrhage rate after last SRS treatment was 3.9% (95% confidence interval, 0.8%-11.5%). Radiation-induced adverse effects occurred in 2 patients.ConclusionsIn our series, volume-staged SRS for AVMs >20 cm(3) achieved a nidus obliteration rate of 35% at 5 years. There was still a high risk for hemorrhage (∼ 4% per year) after treatment, which seemed to be higher than the rate commonly observed in the posttreatment course of single-session SRS for average-size AVMs. Further cases will help determine whether volume-staged SRS could be routinely considered, based on its efficacy and risks, including comparison with the natural history of large AVMs.Copyright © 2016 Elsevier Inc. All rights reserved.

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